The present invention pertains to articles and methods that generate repulsive forces and/or alternating repulsive/attractive forces.
It is a well-known consequence of quantum field theory that two neutral, polarizable objects attract each other via forces that are generally referred to as dispersion forces. Examples of such forces include the van der Waals force, the Casimir force, and the Casimir-Polder force. Such forces are responsible, wholly or in part, for the mutual attraction of atoms and molecules at relatively large distances from each other, for the attraction of neutral atoms to surfaces, and for the attraction between two polished surfaces at sub-micron distances.
This last phenomenon manifests itself in the area of micro-electro-mechanical systems (MEMS) engineering as an unwanted latching of micron-sized parts to one another during fabrication and operation. Such latching, commonly referred to as stiction, has been and remains a roadblock to the development or proper functioning of micro-devices since it is usually impossible to separate the parts involved once stiction occurs. Special fabrication techniques are employed to reduce the incidence of stiction during fabrication. And avoiding stiction during normal operation usually requires that the structural properties of a micro-device satisfy some basic requirements of rigidity and a minimum spacing between parts.
Efforts that have been directed to the characterization and control of stiction have tended to view the underlying dispersion forces that are responsible for the problem as xe2x80x9cfacts-of-life.xe2x80x9d Such efforts tend, therefore, to proceed by avoiding or working around dispersion forces through trial and error with appropriate design and fabrication approaches.
The solution to the problem of stiction remains elusive, and the art would benefit from new control methodologies.
Some embodiments of the present invention provide a method and apparatus for controlling or modulating the direction and/or magnitude of dispersion forces (e.g., Casimir force, etc.) between two bodies. Such dispersion forces are responsible for stiction, among other phenomena.
In accordance with the illustrative embodiment, an apparatus for modulating dispersion force gives rise to a repulsive Casimir force by placing two bodies (e.g., two plates, etc.) in near-proximity to one another, wherein, for one of the bodies, dielectric properties predominate; for the other, magnetic properties predominate. The apparatus further includes a device that alters the dielectric or magnetic properties of the bodies. By altering the dielectric or magnetic properties of at least one of the bodies, the repulsive Casimir force can be made to decrease, or vanish, or reappear as an attractive Casimir force.
In one variation of the illustrative embodiment, the altered property is a dielectric property, such as the concentration of free charge carriers in one of the bodies. The concentration of free-charge carriers is altered, for example, by illuminating the body, or changing the temperature of the body, or injecting charge directly into the body, etc. If the concentration of free-charge carriers is the altered property, then the device that alters that property is a laser (for illumination), or a heater/cooler (for changing temperature), or a controlled charge source (for injecting charge).
Modulating the Casimir force in this manner can be used to control stiction in MEMS devices and to accelerate particles, among many other applications.